Optical apparatus for inspecting the contour of articles



F 1954 J. WALKER ET AL 2,668,475

OPTICAL APPARATUS FOR' INSPECTING THE CONTOUR OF ARTICLES Fi led Dec. 10, 1951 Wis/Wa ls JACK WALKER PE/Vfl/ULK LEO/G Patented Feb. 9, 1954 UPTICAL'APPARATUS FOR IN SPECTING'THE "CONTOUR F ARTICLES Jack 'WaIkerEand -Bennock Leng, Coventry, Enggland, assig-nors .to Armstrong Siddeley Motors :Limited, (Joventry, England Application December 10, 1951,"-Ser ial -No. 260;786

. 3 Claims.

This invention relates to an opticalapparatus for use iniinspecting, :or comparing with a'mark- .ing'or picture of the outline of a master, .a-con- :tour'of a turbine blade :or other :art-icle,'.of the ikindin which .just the portion :of the surfaceof -:-the'article1to be .dealt with (suchportion being provided with .:a surface giving diffused reflection) .is brightly illuminated by "means :of light sources angularly disposed in :a plane round it,

the light rays emanating from the :illuminated portion being arranged to reach an objective 'lens'xneans from which they are projected on to 'aa screen'asaa magnified image.

Our object is .-toprovide ,:an inexpensive apparatus of this .kind, and, in particular, an ar- -rangement .of the light sources, which can be used in'connection with a standard form of projector, object lens means; and-screen.

According to :the invention, :the light "sources .are "high pressure dischargelamps in which'the alignmenttof -the arcisicritically maintained,:and in icombination therewith are two substantially :paralleliplates .spaced'fromone another to a predetermined-extent and with the "central plane of the space coinciding with that rofithe lightsources, the plateshaving'openings in them to receive the article with the said portion of its surface in the said plane.

I-n' -the accompanying drawings:

Figure .lis aside elevation of an apparatus according .to the invention, also showing a screen .on to whichthe image is projected;

Figure 215 a vertical section through the means for illuminating an object to beinspected, ;'the

section being on'the' line '2"2 of Figure 3;

Figure 3 is a section on the line 33 of Figure 2; and

Figure 4 indicates the form of image of the object (e. g., a turbine blade) received on the screen.

The apparatus shown includes a base I l on which is supported, through an upright l2, a standard form of projector l3, and a holder, indicated generally at l4, for an object to be inspected (e. g., a turbine blade I5 in the example shown). The illuminating arrangement has a frame tube [6 of which one end can be slid over a tubular portion ll of the projector for supporting purposes and by which focusing can be effected..

To the other end of the frame tube I6 is secured, as by screws 50, the front wall I8 of a generally rectangular casing of which the axis is coaxial with the frame tube. The casing serves as a housing for four angularly-spaced mercury vapour discharge lamps H), which are mounted fromgposts 5| fast withthe wall Iii and which are of the kind having the alignment of the arcs .critically maintained. As will be well understood, -each lamp is in series with-its own choke,

all the lamps being connected in parallel.

The front wall i=8 has an opening in itcoextensive with the bore of the frame tube, and, at its periphery, an axially-directed Wall 20 which is held in position by nutsand bolts-2 1.

Within the casing are-two plates 22, 23 which are closely spaced by spacers -24, and'held together by .nuts andbolts 25. The plate 22 is fast with a sleeve 26 having a sliding engagement with the interiorof the frame tube 1:6, and by=axia1 adjustment of the sleeve-in-the frame tube the central plane of the space-between the plates 22,23 can be made to be coincident-with the plane containing'the-arcs of the lamps. The sleeve :Ziladditionally serves toscreen from thelight rays the forward end of the article under examination.

The article is held by the holder l4 in coaxial holes 2211,2311. in the :plates, and the rear of the article is'screened from the light rays by means vof an axially-extending flange 2? which is fast with theplate23, as by thelnuts and bolts 25, and

extends throughanopening 28 in the rear wall 2910f the casing. The flange 21 provides access to the interior of-the casing for the insertion of the article which is to be=examined.

At the bottomof the casing are holes (not shown) serving as an inletfor cooling air, and at the top thereof there are holes 3| leading to a chimney .30 through which the cooling air may leave. If desired, abafile, indicated in Figure l .at -52, can-:bepprovided withinthe casing forzpreventing emission of light through the air inlet holes, and the chimney outlet can be turned through an angle, as shown, for the like purpose.

For examining an article, such as the turbine blade l5 shown, the article is first coated with, for example, deposited magnesium vapour so as to render the surface suitable for reflecting the sheet of incident light in a diffused manner. By appropriately adjusting the axial position of the frame tube, focusing can be effected of the edge of the illuminated band of the article which is nearer to the objective lens of the projector. An operative ray of the focused edge of the band is indicated at 32 in Figure 2, and the diffused reflection from the illuminated band passes through the projector 3 to produce on a screen 33 an illuminated zone 34 of which the inner periphery is formed by the focused edge and defines the exact shape of the section of the article under examination. The holder I4 is of any suitable form which will enable the article (5 to be adjusted axially for examination of different axial zones, and also enable the position of the article to be adjusted in two directions at right-angles for centering, or otherwise desirably disposing it in the openings 22a, 23a.

By arranging for the negative post 5! of each lamp to be in the inward path of the plate 22 and of a sufiicient length, they can act as stops, during longitudinal adjustment of the plates.

According to the article to be examined, or for desirably varying the width of the illuminated band of the article, the spacers 24 can be substituted by others of a different thickness.

It will be understood that more, or less than the four lamps l9 mentioned can be provided, and also that suitable reflectors can be positioned within the casing for reflecting radially-outward light emission from the lamps to between the two plates in the intervals between adjacent lamps.

What we claim as our invention and desire to secure by Letters Patent of the United States is:

1. An optical apparatus for inspecting the contour of an article, which has a matt surface, by light diffusedly reflected from the article through a projector on to a screen, comprising a casing having at one side an opening; a frame tube fast with said casing and concentrically disposed about said opening, said frame tube adapted for connection to the projector; a pair of spaced parallel opaque plates within said casing, said plates having registering central holes for the reception axially therein of the article to be examined and in alignment with said frame tube, one of said plates having a tube concentrically about its hole, said plate tube slidably guided within said frame tube, whereby said plates can be axially adjusted within said casing, the other of said plates having an axial peripheral flange extending through an opening in the opposite side of said casing; a ring of high pressure discharge lamps fixedly mounted in said casing and arranged for their arcs to be co-planar and disposed about the plates such that the plane of said arcs is coincident with the central plane of the space between said plates for obtaining a localised plane of illumination about the article to be examined, whilst said plate tube and said flange screen the article from all light except that passing between said plates; and means for supporting said article to be within the holes of said plates.

2. An optical apparatus for inspecting the contour of an article, which has a matt surface, by light difiusedly reflected from the article through a projector on to a screen, comprising a casing, having at one side an opening; a frame tube fast with said casing and concentrically disposed about said opening, said frame tube adapted for connection to the projector, a pair of spaced parallel opaque plates within said casing, said plates having registering central holes for the reception axially therein of the article to be examined and in alignment with said frame tube, one of said plates having a tube concentrically about its hole, said plate tube slidably guided within said frame tube, whereby said plates can be axially adjusted within said casing; a ring of high pressure discharge lamps; mountings from said casing for said ring of lamps to hold the latter with their arcs co-planar and disposed about the plates such that the plane of said arcs is coincident with the central plane of the space between said plates for obtaining a localised plane of illumination about the article to be examined.

3. An optical apparatus for inspecting the surface contour of an article having a matt surface, by light diffusedly reflected from the article through a projector on to a screen, comprising a pair of spaced parallel opaque plates having central openings therethrough in axial registry with one another and with the lens of said projector, a frame about said plates, a forward light shield carried by one of said plates and being telescopically receivable through a portion of said frame, a rear light shield carried by the other of said plates and extending through the rear of said frame, means for joining said plates in spaced relationship, a source of high intensity light rays generated within said frame and directed radially inwardly and circumferentially through the spacing between said plates upon the surface to be inspected and means for supporting the article the surface contour of which is to be inspected within the openings of said plates coaxially therewith whereby only the portion of the article in registry with the space between said front and rear plates will be illuminated by said light source.

JACK WALKER. PENNOCK LENG.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,837,979 Mensman Dec. 22, 1931 2,574,119 Mutter Nov. 6, 1951 2,607,267 Fultz Aug. 19,1952 

